Iodotyrosine deiodinase. Further purification of the detergent-solubilized enzyme will be attempted using gel filtration and isoelectric focussing techniques. Purification of the cosolubilized putative redox carrier will be attempted and its functional role, particularly in relation to NADPH-cytochrome c reductase, will be identified. The steapsin-solubilized and purified enzyme will be further characterized in regard to catalytic sites, redox functions, and effects of antibody to the enzyme (to be developed in rabbits) upon enzymatic activity. Conversion of T4 to T3. A comprehensive method for purification of kidney plasma membranes, free from microsomal combination will be attempted with a view to unequivocal subcellular localization of the enzyme. The cholate-solubilized enzyme will be subjected to further purification procedures and the mechanism of 5'-deiodination of T4 will be studied with the purified enzyme. Thiol-dependency of the enzyme and the effect of thiols on reversing PTU-inhibition of 5'-deiodination will be investigated, as well as mechanisms of rT3 inhibition of T4 deiodination. The role of cellular calcium levels in modulating epinephrine-induced lipolysis in fat cells from normal, hypo- or hyperthryoid rats will be investigated. Membrane-binding of Ca as well as studies of Ca influx and efflux with adipocytes under various conditions in relation to thyroid status will be done. The possible involvement of a Ca-dependent phosphodiesterase activating protein in regulating epinephrine-induced cyclic AMP levels in adipocytes will be studied. BIBLIOGRAPHIC REFERENCES: Goswami, A. and I.N. Rosenberg. Studies on a soluble thyroid iodotyrosine deiodinase: activation by NADPH and electron carriers. Endocrinology 101: August, 1977. Rosenberg, I.N. The thyroid. In Keefer-Wilkins Textbook of Medicine, 1977, Little Brown, in press.